NEW YORK (AP) — The FBI is investigating a hacking attack on JPMorgan Chase and at least one other bank, according to reports citing unnamed sources familiar with the matter.

A report on Bloomberg.com said Wednesday that the FBI is investigating an incident in which Russian hackers attacked the U.S financial system earlier this month in possible retaliation against U.S. government-sponsored sanctions aimed at Russia. The attack, Bloomberg said, led to the loss of sensitive data. Bloomberg cited security experts saying that the attack appeared “far beyond the capability of ordinary criminal hackers.”